[R-390] R-390A RF Amplifier 6DC6

[Larry Haney]

Hi Byron,  Good question.  A few years ago, I tried all of the
possible substitutions for it and came to the conclusion that they did not
improve the s/n test.  And, they all deteriorated the operation of the
Carrier Level meter.  See my doc on our website on page 2 for more info: R390A
Fix Non-Linear CL Mtr.pdf (r-390a.net)
<https://www.r-390a.net/R390A%20Fix%20Non-Linear%20CL%20Mtr.pdf>.

The following info about 6DC6's is from Jacques Fortin:

For your “Philips” 6DC6s, would you mean ECG-Philips ones (formerly
Sylvania) of some European-made Philips branded ones ??

Maybe they were not made as “real” 6DC6… rebranded 6BZ6 ??

Or maybe worse: I have one 6DC6 with an etched-in-glass number, no brand,
but on the flip side, you can still read, very faint, in the RCA numbering
style: 6CB6A !

And guess what: this unit tests as a sharp-cutoff tube, not a semi-remote
cutoff one…


The net of it is that you should use a 6DC6 of the brand that provides the
best s/n and Carrier Level meter operation.


Regards, Larry



On Sat, Jun 29, 2024 at 7:23 PM Byron Tatum <bjtatum1 at att.net> wrote:

> Hello-    If I can impose for some more tube advice or commentary. I have
> read in more than one post that some prefer the 6BZ6/6JH6 in place of 6DC6
> for RF amp in the R-390A. I have been through many of these receivers over
> the years and have found the 6BZ6 in that spot in some.    Does anyone have
> any supporting evidence for this substitution, or experiment results from
> subbing? I don't like to sub tube types and feel the design engineers chose
> the 6DC6 for a good reason. I myself have not played around with this
> substitution yet.Thanks,Byron W5FH
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